The present invention relates to a mechanical actuator, but more specifically to an electronically controlled pneumatic actuator formed on a substrate, such as a PC board.
Positional control of an object, such as in robotics applications, requires the ability to sense forces acting on and the motion of the object, to exert a force on the object, and/or to perform computations necessary to effectuate control of an actuator that drives the object. While significant progress has been made in the sensing and computational field, developments directed to actuator driving mechanisms have been lacking. It is not known in prior art, for example, how to fully emulate human muscle behavior to move an object.
Desirable actuator characteristics include low-cost, low mass, low power consumption, large range or stroke of operation, small volume, and ease and efficiency of energy conversion to perform mechanical work. Low mass reduces the amount of force required to move the object, thus reducing power consumption. Actuators having these characteristics are particularly suited for use in small force robotic applications and elsewhere that require low mass actuators.
Planar pneumatic muscles have many advantages including ready adaptability to PC Board fabrication techniques. Complex arrays of pneumatic muscle actuators can also be fabricated at reasonable costs. In addition, electrical connections between pneumatic muscles and controllers are easily implemented.
Pneumatic muscles also have lower mass. This contrasts with relatively heavier electric motors that have iron cores and solenoid actuators that have copper windings, for example. Hydraulic actuator systems require seals and containment walls of relatively high mass, which often interfere with the mechanical structure and operation. Pneumatic muscles, on the other hand, have notably low mass, thereby permitting high-speed operations that are frequently required in robotics applications.
In addition, tolerances for fabricating pneumatic muscles are somewhat relaxed in comparison to hydraulic systems because pressure leaks are not believed to be as critical. Moreover, leaks of pressurizing gases, such as air, are less likely to damage surrounding components or endanger the environment or human health. Pneumatic muscle also efficiently converts power to mechanical work.
Pneumatic muscle systems may also be designed with notably large strokes and working ranges. If air is used as a pressuring gas, the force remains relatively constant over the entire stroke range, unlike many mechanical systems. For example, a solenoid actuator requires conventional cores of increasingly greater mass or as the stroke distance increases. A solenoid actuator having a stroke of thirty centimeters, for example, would have significant mass.
Pneumatic muscles fabricated on a PC board can be switched at relatively low pressure levels, e.g., 1 kPa. If electrostatic PC board valves were replaced by electromagnetic solenoid valves, higher pressures of perhaps up to 1 MPa could be achieved thereby permitting larger forces. Electromagnetic solenoid valves can be fabricated using PC Board technology or using impact printer technology. Smaller solenoid air valves are heavier, but not as heavy as corresponding motors required to perform equivalent work.
In accordance with one aspect of the invention, a pneumatic actuator formed on a PC board produces a force that acts on an object and preferably includes a first pressure source providing a first pressure, a second pressure source providing a second pressure lower than the first source, at least one expansion chamber alternately communicating with the first and second pressure sources, first and second valves formed on the substrate that controllably open and close the chamber with respect to one of the first and second pressure sources, and an actuator member interacting with the expansion chamber to apply a force to the object. The actuator is preferably formed using planar batch technology and the valves preferably comprise electrically controllable flap valves mounted on the PC board.
In another embodiment of the invention, the actuator includes antagonistically arranged expansion chambers that operatively produce and apply reciprocating forces to the object, thereby to move the object in an oscillating manner. In yet other embodiments, the actuator includes plural expansion chambers arranged in series or in parallel in order to increase the overall extent of attainable displacement or to amplify the force generated by the actuator.
According to another aspect of the invention, a pneumatic actuator that emulates a muscle (hereafter, a xe2x80x9cpneumatic musclexe2x80x9d) uses electronically controlled air valves to generate contraction forces. Reciprocal motion is achieved by using pneumatic muscles or expansion chambers thereof in antagonistic pairs. Valves are fabricated using PC board fabrication techniques in order to minimize costs, simplify communication between the muscle and controller, and minimize weight and volume of valves. PC board fabrication also permits complex combinations of valves, as well as the ability to incorporate valves with flexible substrates.
Other features, aspects, and advantages of the invention will become apparent upon review of the following description taken in connection with the accompanying drawings. The invention, though, is pointed out with particularity by the appended claims.